ENEL´s experience with on line partial discharge measurement on stator windings of large synchronous hydro generators

Results of work in progress at ENEL concerning online measurement of partial discharges in the stator windings of large synchronous hydro generators are reported. The guidelines of this work are basically in accordance with the technique developed by the Ontario Hydro Research Division. Capacitive couplers were set up and permanently installed on the stator windings and/or on the busbars of some 15 hydro generators rated in the range of 50-200 MVA. The main characteristics of these couplers are given, and the basic criteria followed for their installation are briefly reviewed. Pulse waveshapes recorded during operation of the generators are shown, and signals coming from couplers located at different points are compared. Attention is also given to signals resulting from coupling systems installed both inside a generator and along the busbars. Examples of results of online partial discharge measurements performed using a commercially available analyzer are provided